Viscosity of Ionic Liquids: Theories and Models

Area of Science:

• Physical Chemistry
• Materials Science
• Chemical Engineering

Background:

• Ionic liquids (ILs) possess unique, tunable properties making them superior to conventional solvents.
• Accurate prediction of ILs' pressure-viscosity-temperature (P-η-T) behavior is crucial for their wider application.
• Existing models for IL viscosity require systematic evaluation and comparison.

Purpose of the Study:

• To review and quantitatively assess theoretical and empirical models for IL viscosity.
• To introduce methods for calculating thermodynamic inputs for viscosity models.
• To propose predictive equations for IL-related mixture viscosity.

Main Methods:

• Introduction of thermodynamic calculation methods for viscosity models.
• Review of theories, theoretical, semi-empirical, empirical, and phenomenological models for IL viscosity.
• Systematic comparison of model performance for pure ILs and IL-related mixtures.

Main Results:

• Evaluation of various modeling approaches, including those coupling theories with EoSs or activity coefficient models.
• Proposal of simple predictive equations for the viscosity of IL-related mixtures.
• Comparison of the predictive capabilities of different viscosity models.

Conclusions:

• Recommendation of robust predictive models for IL viscosity at atmospheric pressure.
• Identification of consistent theories and models for P-η-T behavior.
• Outline of remaining research challenges in IL viscosity modeling.